When I switch back to using the sandbox environment endpoint (https://platform.devtest.ringcentral.com/restapi/oauth/token) everything works perfectly.

I know I have different credentials for both the production and sandbox environments.

I took my Client ID & Client Secret for my Production Environment and base64 encoded them in the format {{client_id}}:{{client_secret}} from https://www.base64decode.org.

These are the same exact steps that worked successfully for me in the sandbox environment but it says my client id is invalid in production... I did a string comparison for the {{my_client_id}} value returned in the error response above and compared it to my Production Environment Client ID in the web console and they match exactly, so I am not sure what to do at this point.

I thought that it was maybe because I am trying to access this production environment endpoint shortly after graduating my app to production, but after a few hours, it still does not work.

This answer came as a result of a tech support session with RingCentral engineers, and several days worth of them troubleshooting the issue. I did not find this answer, or any reference to this URL, anywhere in this forum.

Hope this can help others avoid some headaches when moving their app to production.

I login with my email and password(not a phone number if that makes a difference) and my username/password for production is the same as my sandbox credentials.

I receive a 404 error for the link you provided when I try to open it in my browser, however I am able to login to the admin portal with the exact same username/password as my developer account.

Also, if I change my user credentials to be incorrect, I receive the error "Invalid resource owner credentials", so it seems like it is getting past my user credentials and failing when it checks my client id.

Since the solution you mentioned is no where documented and most of the user is also not aware about the url format you mentioned in the solution, request ringCentral team to justify the solution and document somewhere so that it can be referred in future.

I am also receiving this response: OAU-153 Invalid client: ZQKpuJrXQ82jGxt0_4w-4A

And this client reported is exactly the same one as in my sandbox console. In the past I would only get this error if the client ID was incorrect OR the API server URL is incorrect. But I have copy - pasted them from the console.